Spanish phonology and American accents
Among native speakers of American English who are learning Spanish, there’s a natural error that can easily mark them out as non-native Spanish speakers, and that seems to be fairly common. It’s all about the pronunciation and behaviour of the coronal consonants /t/ and /d/.
In most North American varieties of English, both /t/ and /d/ are realised as [ɾ] between vowels, except when the consonant is the onset of the stressed syllable in the word. This can be regarded as a form of intervocalic consonant lenition. (That’s a slight simplification; the Wikipedia page on this process has more details.)
Spanish has the same two phonemes /t/ and /d/, but their behaviour is rather different. (At least according to my understanding, though I should clarify that my Spanish is rudimentary.) Of those, /t/ is realised as a neutral, non-aspirated [t] in all contexts. On the other hand, /d/ is realised as [ð] intervocalically, and as a heavily voiced [d̬] word-initially. Again, the realisation of /d/ as [ð] can be regarded as a form of lenition.
So what’s the common error? Well, American English phonology merges /t/ and /d/ in intervocalic contexts. Once learners have acquired enough Spanish phonology to know that intervocalic coronal lenition produces [ð] for /d/ in that context — that is, to know that nada ‘nothing’ is [ˈnaða] — there’s a strong tendency to combine Spanish lenition with its near-equivalent in English. The /d/→[ð] gets overapplied to /t/ (since those phonemes are merged in English), incorrectly yielding [ð] intervocalically.
I encountered an excellent example of this recently. I was watching an episode of Without a Trace that featured Camille Guaty as someone who comes from Guatemala. Ms Guaty’s Spanish-accented English seemed fine for the most part, but very early on, she said something that gave me pause: she named her character’s country of origin as [ˌgwaðeˈmala].
That one word was enough to convince me that Ms Guaty is not a native Spanish speaker (or that if she is, her dialect is an unusual one, probably learned in a predominantly American-English–speaking environment). Googling didn’t reveal anything that conflicted with my suppositions; we have for a example a fan site saying that she was “born in California” and that “[s]he and her family moved to New Jersey when she was five years old”.